PLATE 1 



EXPLANATION OF FIGURES 



1 Section of a testis of a guinea-chicken hybrid showing the narrow, atrophied 

 seminiferous tubules separated by wide areas of interstitial substance. X 75. 



2 Section of a testis of a guinea-chicken hybrid showing an island-like mass of 

 seminiferous tubules, normal in size, in a broad field of connective tissue and 

 stroma cells. X 75. 



3 Section showing an area of the testis in one of the guinea-chicken hybrids in 

 which, in places, the seminiferous tubules were almost as plentiful as in normal 

 non-hybrid individuals. X 75. 



4 Section of a testis of a guinea-chicken hybrid showing an inter-tubular area 

 in which numerous cells were in various stages of maturation. Primary spermato- 

 cytes in process of division were not uncommon. X 75. 



5 Metaphase of a dividing first spermatocyte of the langshan cock, fig. 5i 

 being at a magnification of 750, and 56, 1500 diameters. The typical U-shaped 

 element appears to be more of a V in the photograph, but this is due to the fact 

 that when the ends of the chromosome were in focus as they are in the photograph, 

 the bend of the U was depressed below the plane of focus, giving to the picture a 

 sharp-angled appearance which the real object did not possess. 



6 Metaphase of a dividing first spermatocyte of the guinea, viewed from one 

 pole. The X-element is at the top and is plainly seen to be narrower at one end 

 than at the other. It lay in such a position that its curved condition could not be 

 shown by photography. X 1500. 



7 Metaphase of a dividing first spermatocyte of the hybrid, viewed from one 

 pole. What appears to be a long curved body at the top consists really of two chro- 

 mosomes; one, at the base, a deeply-staining, rounded, ordinary chromosome, and 

 the other the curved X-element. To show the curve of the latter the camera had 

 to be so focussed as to blend the two images. Like that of the guinea, the X-ele- 

 ment of the hybrid is seen to be narrower at one end. X 1500. 



8 Side view of a first spermatocyte in the hybrid showing the cell ready for divi- 

 sion with the X-element lying just above the level of the regular equatorial plate 

 of chromosomes. The photograph does not reveal the curved shape of the ele- 

 ment although this could readily be detected by manipulation of the fine adjust- 

 ment of the microscope. X 1500. 



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